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2Computer Programming I
Outline Variables and Assignments Identifiers Keywords Input and Output Data Types and Expressions Arithmetic
3Computer Programming I
Variables and Assignments Variables are like small blackboards
We can write a number on them We can change the number We can erase the number
C++ variables are names for memory locations We can write a value in them We can change the value stored there We cannot erase the memory location
Some value is always there (old content)
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Identifiers Variables names are called identifiers Each piece of data in the computer is
stored at a unique memory address Identifier names allow us to symbolically
deal with the memory locations so that we don’t have to deal directly with these addresses e.g. total instead of 1001110001110001
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Identifiers
char = 1 byte
0000
0001
0003
0002
0007
0005
0008
0010
0009
0012
0011
0013
0014
x is an integer variable
int x;
char c1, c2;
c1 and c2 are character variable
f1 is a float variable
float f1;
4 bytes
4 bytes
Memory Address
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Choosing variable names Use meaningful names that represent data to
be stored First character must be
a letter (a-z, A-Z) the underscore character (_)
Remaining characters must be letters Numbers (letter (0-9) underscore character
Identifiers
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Keywords Keywords (also called reserved words)
Are used by the C++ language Must be used as they are defined in
the programming language Cannot be used as identifiers
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Declaring Variables Before use,,, variables must be declared
Tells the compiler the type of data to store
Examples: int number_of_boxes; double one_weight, total_weight;
int is an abbreviation for integer. could store 3, 102, 3211, -456, etc. number_of_boxes is of type integer
double represents numbers with a fractional component could store 1.34, 4.0, -345.6, etc. one_weight and total_weight are both of type double
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Declaring Variables
Declaration syntax: Type_name Variable_1 , Variable_2, . . . ;
Declaration Examples: double average, m_score, total_score; double moon_distance; int age, num_students; int cars_waiting;
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Assignment Statements An assignment statement changes the value of a
variable total_weight = one_weight + number_of_bars;
total_weight is set to the sum one_weight + number_of_bars
Assignment statements end with a semi-colon
The single variable to be changed is always on the leftof the assignment operator ‘=‘
On the right of the assignment operator can be Constants – age = 21; Variables -- my_cost = your_cost; Expressions – circumference = diameter * 3.14159;
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Initializing Variables Declaring a variable does not give it a value
Giving a variable its first value is initializing the variable Variables are initialized in assignment statements
double mpg; // declare the variable mpg = 26.3; // initialize the variable
Declaration and initialization can be combinedusing two methods Method 1
double mpg = 26.3, area = 0.0 , volume; Method 2
double mpg(26.3), area(0.0), volume;
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Input and Output A data stream is a sequence of data
Typically in the form of characters or numbers
An input stream is data for the program to use Typically originates
at the keyboard at a file
An output stream is the program’s output Destination is typically
the monitor a file
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Output using cout
cout is an output stream sending data to the monitor
The insertion operator "<<" inserts data into cout Example:
cout << number_of_box << " candy bars\n"; This line sends two items to the monitor
The value of number_of_box The quoted string of characters " candy bars\n"
Notice the space before the ‘c’ in candy The ‘\n’ causes a new line to be started following the ‘s’ in bars
A new insertion operator is used for each item of output
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Examples Using cout This produces the same result as the previous sample
cout << number_of_bars ;cout << " candy bars\n";
Here arithmetic is performed in the cout statementcout << "Total cost is $" << (price + tax);
Quoted strings are enclosed in double quotes ("Walter") Don’t use two single quotes (')
A blank space can also be inserted with
cout << " " ;
if there are no strings in which a space is desired as in " candy bars\n"
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Escape Sequences Escape sequences tell the compiler to treat
characters in a special way '\' is the escape character
To create a newline in output use \n – cout << "\n"; or the newer alternative cout << endl;
Other escape sequences: \t -- a tab \\ -- a backslash character \" -- a quote character
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Escape SequencesASCII char Symbolic Name
Null character
Alert (bell)
Backspace
Horizontal tab
New line
Vertical tab
Form feed
Carriage
return
Single quote
Double quote
Backslash
‘\0’
‘\a’
‘\b’
‘\t’
‘\n’
‘\v’
‘\f’
‘\r’
‘\’’
‘\”’
‘\\’
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Formatting Real Numbers Real numbers (type double) produce a variety of
outputs
double price = 78.5;cout << "The price is $" << price << endl;
The output could be any of these: The price is $78.5 The price is $78.500000
The price is $7.850000e01 The most unlikely output is:
The price is $78.50
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Showing Decimal Places cout includes tools to specify the output of type double
To specify fixed point notation setf(ios::fixed)
To specify that the decimal point will always be shown setf(ios::showpoint)
To specify that two decimal places will always be shown precision(2)
Example: cout.setf (ios::fixed);cout.setf (ios::showpoint);cout.precision (2);cout << "The price is " << 1.234 << endl;
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Input Using cin cin is an input stream bringing data from the keyboard The extraction operator (>>) removes data to be used Example:
cout << "Enter the number of bars in a package\n"; cout << " and the weight in ounces of one bar.\n"; cin >> number_of_box; cin >> one_weight;
This code prompts the user to enter data thenreads two data items from cin The first value read is stored in number_of_bars The second value read is stored in one_weight Data is separated by spaces when entered
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Reading Data From cin Multiple data items are separated by spaces Data is not read until the enter key is pressed
Allows user to make corrections
Example: cin >> v1 >> v2 >> v3;
Requires three space separated values User might type
34 45 12 <enter key>
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Designing Input and Output
Prompt the user for input that is desired cout statements provide instructions
cout << "Enter your age: ";cin >> age;
Notice the absence of a new line before using cin
Echo the input by displaying what was read Gives the user a chance to verify data
cout << age << " was entered." << endl;
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Data Types and Expressions
2 and 2.0 are not the same number A whole number such as 2 is of type int A real number such as 2.0 is of type double
Numbers of type int are stored as exact values Numbers of type double may be stored as
approximatevalues due to limitations on number of significant digits that can be represented
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Writing Integer constants Type int does not contain decimal points
Examples: 34 45 1 89
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Writing Double Constants Type double can be written in two ways
Simple form must include a decimal point Examples: 34.1 23.0034 1.0 89.9
Floating Point Notation (Scientific Notation) Examples: 3.41e1 means 34.1
3.67e17 means 367000000000000000.0 5.89e-6 means 0.00000589
Number left of e does not require a decimal point Exponent cannot contain a decimal point
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Other Number Types Various number types have different
memory requirements More precision requires more bytes of memory Very large numbers require more bytes of
memory Very small numbers require more bytes of
memory
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Some number typesType Name Memory Used Size Range Precision
short 2 bytes -32,767 to 32,767
NA
int 4 bytes -2,147,483,647 to 2,147,483,647
NA
long 4 bytes -2,147,483,647 to 2,147,483,647
NA
float 4 bytes Approximately 10-38 to 1038
7 digits
double 8 bytes Approximately 10-308 to 10308
15 digits
long double 10 bytes Approximately 10-4932 to 104932
19 digits
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Integer types long or long int (often 4 bytes)
Equivalent forms to declare very large integers
long big_total;long int big_total;
short or short int (often 2 bytes) Equivalent forms to declare smaller integers
short small_total; short int small_total;
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Floating point types long double (often 10 bytes)
Declares floating point numbers with up to 19 significant digits
long double big_number;
float (often 4 bytes) Declares floating point numbers with up to
7 significant digits
float not_so_big_number;
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Type char Computers process character data too char
Short for character Can be any single character from the keyboard
To declare a variable of type char:
char letter;
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char constants Character constants are enclosed in single quotes
char letter = 'a';
Strings of characters, even if only one characteris enclosed in double quotes "a" is a string of characters containing one character 'a' is a value of type character
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Reading Character Data cin skips blanks and line breaks looking for data The following reads two characters but skips
any space that might be between
char symbol1, symbol2; cin >> symbol1 >> symbol2;
User normally separate data items by spaces J D
Results are the same if the data is not separated by spaces
JD
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Type bool bool is a new addition to C++
Short for boolean Boolean values are either true or false
To declare a variable of type bool:
bool old_enough;
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Type Compatibilities In general store values in variables of the
same type This is a type mismatch:
int int_variable;
int_variable = 2.99;
If your compiler allows this, int_variable willmost likely contain the value 2, not 2.99
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int double Variables of type double should not be
assigned to variables of type int
int int_variable; double double_variable; double_variable = 2.00; int_variable = double_variable;
If allowed, int_variable contains 2, not 2.00
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int double Integer values can normally be stored in
variables of type double
double double_variable; double_variable = 2;
double_variable will contain 2.0
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char int The following actions are possible but
generally not recommended! It is possible to store char values in integer
variables int value = 'A';value will contain an integer representing 'A'
It is possible to store int values in charvariables char letter = 65;
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bool int The following actions are possible but generally
not recommended! Values of type bool can be assigned to int
variables True is stored as 1 False is stored as 0
Values of type int can be assigned to boolvariables Any non-zero integer is stored as true Zero is stored as false
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Arithmetic Arithmetic is performed with operators
+ for addition - for subtraction * for multiplication / for division
Example: storing a product in the variable total_weight
total_weight = one_weight * number_of_bars;
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Results of Operators Arithmetic operators can be used with any
numeric type An operand is a number or variable
used by the operator Result of an operator depends on the types
of operands If both operands are int, the result is int If one or both operands are double, the result is
double
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Division of Doubles Division with at least one operator of type double
produces the expected results.
double divisor, dividend, quotient; divisor = 3; dividend = 5; quotient = dividend / divisor;
quotient = 1.6666… Result is the same if either dividend or divisor is
of type int
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Division of Integers Be careful with the division operator!
int / int produces an integer result (true for variables or numeric constants)
int dividend, divisor, quotient; dividend = 5; divisor = 3; quotient = dividend / divisor;
The value of quotient is 1, not 1.666… Integer division does not round the result, the
fractional part is discarded!
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Integer Remainders %(mod) operator gives the remainder from
integer division
int dividend, divisor, remainder; dividend = 5; divisor = 3; remainder = dividend % divisor;
The value of remainder is 2
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Arithmetic Expressions Use spacing to make expressions readable
Which is easier to read?
x+y*z or x + y * z
Precedence rules for operators are the same as used in your algebra classes
Use parentheses to alter the order of operations x + y * z ( y is multiplied by z first) (x + y) * z ( x and y are added first)
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Operator Shorthand Some expressions occur so often that C++
contains to shorthand operators for them All arithmetic operators can be used this way
+= count = count + 2; becomes count += 2;
*= bonus = bonus * 2; becomes bonus *= 2;
/= time = time / rush_factor; becomes time /= rush_factor;
%= remainder = remainder % (cnt1+ cnt2); becomes remainder %= (cnt1 + cnt2);
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Increment/Decrement Unary operators require only one operand
+ in front of a number such as +5 - in front of a number such as -5
++ increment operator Adds 1 to the value of a variable
x ++; is equivalent to x = x + 1;
-- decrement operator Subtracts 1 from the value of a variable
x --;is equivalent to x = x – 1;
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Exercises1) X += 1
2) X *= Y
3) X += X – Y * Z
4) X++
5) X *= 2
6) X *= Y * Z
7) X %= X / Y
8) X--
1) X = X + 1
2) X = X * Y
3) X = X + ( X – Y * Z )
4) X =X + 1
5) X = X * 2
6) X = X * Y * Z
7) X=X % ( X / Y )
8) X =X - 1
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Precedence Operators Precedence
Postfix ++, -- Highest
Lowest
Prefix ++, --Unary +,-*, /, %
Binary +, -
<, <=, >=, >
= =, !=
&&
| |
=
Parentheses ( )
Precedence Table
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Math Symbol English C++ Notation
C++ Sample
= equal to = = x + 7 = = 2*y
≠ not equal to != Abc != ’n’
< less than < count < m + 3
≤ less than or equal to <= time <= limit
> greater than > time > limit
≥ greater than or equal to
>= age >= 21
Comparison Operators